Sensitivity characteristics near the dispersion turning points of long-period fiber gratings in B/Ge codoped fiber

We report a theoretical and experimental investigation of the dispersion pr operty of long-period fiber gratings in B/Ge codoped fiber. A novel concept of a mode ultrasensitive zone defined by a region in which the phase-match ing conditions are close to the dispersion turning points is proposed. The transition from a dual-resonance state to a dispersion turning point is rev ealed for a set of ultrasensitive-zone gratings during the UV-writing proce ss. We explore the sensitivity characteristics near the dispersion turning points, with the aim of implementing two types of temperature sensor with s ensitivity 2 orders of magnitude higher than that of the conventional long- period gratings. (C) 2001 Optical Society of America.